A groundbreaking new research project has analyzed the evolution of the placental mammalian skull using 3D scans of 322 specimens housed in more than 20 international museum collections, and devised a new model of how mammals evolved. diversified according to emerging models.
By gathering data on the skulls of all major groups of placental mammals, extinct and extant, the team of researchers led by Professor Anjali Goswami at the Natural History Museum, has acquired a unique look across time and taxa to trace the adaptive radiation (rapid evolution that fills a variety of ecological niches) of mammals and decipher what led to their incredible rise following the extinction of the dinosaurs.
Professor Goswami says: “This research will transform our understanding of the incredible radiation of placental mammals, a group that includes our own species, and how this critical period after the last mass extinction 66 million years ago shaped the evolution since.”
The arrival of the age of mammals
Although the first mammals existed alongside the dinosaurs, their diversity was relatively limited, with the largest mammals of the Mesozoic era reaching the size of a small dog. However, immediately after the extinction of the dinosaurs, there is an incredible explosion of diversity among placental mammals with the earliest ancestors of today’s living groups appearing in the fossil record some 100,000 years after this event.
However, this new study shows that after the initial burst of mammalian diversification, the pace of evolution quickly slows. Later bursts of faster evolution occur, but their impacts get smaller and smaller over time and never match the speed of this first peak. Although uncertainty about the exact timing of these later bursts makes it difficult to attribute them to specific events, they are likely caused by periods of rapid or sustained climate change and global cooling during the Cenozoic Era.
The study also shows remarkable similarities or convergence between placental mammals, with most forms of mammalian skulls evolving in roughly the same way in the fossil record. The biggest exceptions are whales and rodents.
What makes mammals evolve rapidly?
One of the main goals of this study is to better predict how different species may react to rapid changes in their environment – the kind we are likely to see throughout the current planetary emergency. To do this, the team studied the characteristics of rapidly changing mammals and found that the main influencing factors were habitat, social behaviors, diet, parental care and activity time.
Social structures greatly differentiate the rate at which mammals evolve. Social mammals evolve much faster than solitary ones. This is easily seen in ungulates which have developed horns and antlers for combat and social display. Mammals that live in aquatic environments, including whales but also manatees, seals and walruses are also changing rapidly. Herbivores also evolve faster than carnivores, probably because they follow changes in plants and the environment more closely than meat eaters.
“I performed most of the analyzes for this paper while isolating myself at home for several months at the start of the COVID-19 pandemic, so seeing the results of the evolution of social mammals versus solitary mammals was really hit,” adds Professor Goswami.
Parental care also appears to be an important factor slowing the rate of evolution. Early animals that require little primary care, such as horses and antelopes, evolve much faster than altricial mammals that depend on caregivers in infancy, such as primates. When animals are active also makes a difference, species with a strict schedule, whether nocturnal or diurnal, evolve more slowly than animals without a fixed activity pattern.
Unexpectedly, the mammalian groups with the most species, rodents and bats, do not appear to evolve very rapidly, suggesting that form diversity and number diversity are not closely related in mammals.
What did the first placental mammals look like and why haven’t scientists found their fossils?
Using this new dataset, the team also pieced together what early placental mammals might have looked like. Although there are many fossil mammals from the correct period, identifying fossils that represent the ancestors or early members of the placental group of mammals, which would have lived in the late Cretaceous, just before the extinction of the dinosaurs, has been a major debate among scientists.
One problem is that it’s hard to know what characteristics to expect in the earliest representatives of any major mammalian group, and whether scientists would recognize them in known fossils. The new reconstructions from this study show that the earliest members of all major placental mammal groups probably looked very similar, whether they were the ancestor of rodents and their close relatives, or elephants and their close relatives. This means that it can continue to be very difficult to identify the earliest placental mammal fossils, but these new reconstructions provide insight into the subtle differences scientists need to look for in these early mammal fossils.
Professor Goswami explains: “The museum’s collections are a unique asset because they allow us to predict the future by looking into the past. About a third of the samples used in this study came from the collections here at the museum, including a nice digitization 3D. of Hope, the blue whale hanging in the museum’s Hintze room. This data is invaluable in helping us understand how past events shaped the evolution of mammals during the Cenozoic Era, and what characteristics will help mammals to survive the environmental challenges that await us.
The study, “Attenuated evolution of mammals through the Cenozoic,” is published in the journal Science Friday, October 28.
Mammals only diversified after dinosaur extinction left space
Anjali Goswami et al, Attenuated evolution of mammals through the Cenozoic, Science (2022). DOI: 10.1126/science.abm7525
Provided by Natural History Museum
This story is republished with the kind permission of the Natural History Museum. Read the original story here.
Quote: Social mammals evolve faster than solitaries, according to a new study on evolution (2022, October 28) retrieved October 29, 2022 from https://phys.org/news/2022-10-social-mammals-evolve -faster-solitary. html
This document is subject to copyright. Except for fair use for purposes of private study or research, no part may be reproduced without written permission. The content is provided for information only.
#Social #mammals #evolve #faster #solitary #evolution #study #finds